This invention claims the benefit of Japanese patent application No. 2001-85090, filed on Mar. 23, 2001, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a lamp for vehicles such as headlamp, a fog lamp, or the like, and more particularly to a projector type lamp. A projector typeamp used herein can be composed of: an ellipsoidal reflector having a first focal point and a second focal point that is formed, for example, as a spheroid-of-revolution surface, or an elliptic free-curved surface; a light source arranged in the vicinity of the first focal point of the reflector; a projection lens arranged with its focal point located in a vicinity of the second focal point on which light emitted from the light source and reflected by the reflector converges; and a shade, as may be required, for controlling light distribution characteristics, arranged in the vicinity of the focal point of the projection lens.
2. Description of the Related Art
An example of a conventional projector type lamp 90 of the type mentioned above is shown in FIG. 13. The projector type lamp 90 is composed of: a reflector 91 which is formed, for example, as a spheroid-of-revolution surface having a first focal point f1 and a second focal point f2; a light source 92 arranged in the vicinity of the first focal point f1 of the reflector 91; and a projection lens 93 arranged such that a focal point f3 thereof is located in the vicinity of the second focal point f2 on which light emitted from the light source 92 and reflected by the reflector 91 converges.
Here, it is preferable to additionally employ a shade 94. Only beams of light required for producing an intended light distribution characteristic are permitted to pass above the shade 94, and unnecessary portions of light that converge on second focal point f2 are blocked thereby. This makes it possible to realize a projector type lamp 90 having appropriate light distribution characteristics such that, for example, when the shade 94 is located in the light path, a passing beam (hereafter referred to as xe2x80x9clow beamxe2x80x9d) is turned on, and, when the shade 94 is retracted from the light path, a driving beam (hereafter referred to as xe2x80x9chigh beamxe2x80x9d) is turned on.
In the conventional projector type lamp 90, however, the light having converged on the second focal point f2 once, and which is expected to diverge radially thereafter, is condensed by the projection lens 93 to such an extent that it is projected in an illumination direction. Thus, the projected light is apt to diverge radially even after passing through the projection lens 93. This makes it difficult to satisfactorily focus light at a desired position.
Accordingly, the projector type lamp 90, though having the advantage of producing a light distribution characteristic of desired profile, particularly of forming a cut-off line of a low beam, has a limited degree of freedom in luminance distribution within the profile of the light distribution characteristic. Thus, the projector type lamp 90 cannot be suitably used as a lamp which illuminates a faraway area more brightly than a front, closer area, such as a headlamp for high-beam distribution.
Moreover, the projection lens 93 appears circular when seen from the front, and, when the projector type lamp 90 is mounted on a vehicle, only the projection lens 93 is visible. Therefore, any lamp of this type provides similar impressions, and it is substantially impossible to render design variations according to the type of a vehicle on which the light is mounted. That is, the conventional projector type lamp 90 has a disadvantage in that it lacks design flexibility.
Further, since the heat produced by the light source 92 is considerably concentrated on the projection lens 93, a sharp temperature rise is inevitable. This necessitates the use of a glass member which is excellent in heat resistance, leading to an increase in cost and making it difficult to achieve weight reduction. These are examples of problems in the art that need to be solved.
Note that, in order to obtain the above-described illumination characteristics, namely, to illuminate a faraway area more brightly than a front area, and to increase the flexibility in design, there has been proposed a horizontally elongated projection lens. This projection lens is formed by cutting end portions in a vertical direction of the projection lens so that it appears substantially oval when viewed in a direction of an optical axis. However, such a horizontally elongated configuration cannot be realized without using an unprocessed projection lens that has a large outer diameter in terms of the need for cutting. The larger the outer diameter of a lens, the greater the thickness. This makes weight reduction very difficult.
In view of the foregoing, an object of the present invention is to provide a projector type lamp having an excellent light illumination characteristic in which a distant area is illuminated more brightly than an area closer to the lamp. The lamp can be made thin and lighter in weight, and have a shape of novel design when seen from the front, that is, offering a differentiating feature in terms of outward appearance, unlike conventional projection lenses. Another object of the present invention is to provide a projector type lamp in which it is possible to use light coming from a reflecting surface, even light which is typically not utilized when using a conventional Fresnel lens (because the light becomes glare light), thus increasing a quantity of light emitted from a vehicle lamp while also reducing weight of the lamp without causing glare light.
To attain the above objects, a projector type lamp according to the present invention can include: an ellipse group reflector having a first focal point and a second focal point; a light source arranged in a vicinity of the first focal point of the reflector; and a projection lens arranged with its focal point located in a vicinity of the second focal point on which light emitted from the light source and reflected by the reflector converges. The projection lens can be formed by combining a plurality of processed projection lens elements that are fabricated by processing a plurality of unprocessed projection lenses that are substantially identical in optical axis center and focal point yet different in outer diameter. The projection lens can have a substantially rectangular shape in a plan view as seen in an optical axis direction. Boundary portions between the plurality of processed projection lens elements in the plan view can be composed of a line connecting points of intersection between a contour line of the projection lens and a line defining part of each unprocessed projection lens at which the thickness of the lens is substantially zero as measured/viewed in the optical axis direction. (Contour lines defined as lines that define the periphery of the projection lens when viewed from the front along the optical axis.) Thereby, lens surfaces of the processed projection lens elements can be continuous with one another through stepped portions. A longitudinal section of each of the stepped portions includes a straight line substantially parallel to the optical axis in a longitudinal section of the projection lens. In other words, the stepped portions are separated from each other by a lens surface that is substantially parallel to the optical axis of the lens.
With this projector type lamp according to the invention, it is possible to obtain an excellent light illumination characteristic in which a distant area is more brightly illuminated than an area closer to the lamp. Moreover, the projection lens can be made slimmer and lighter in weight, and, unlike a conventional circular projection lens, can have a shape of novel design when seen from the front, that is, it can offer a differentiating feature in terms of outward appearance. Further, the junctions among the lens surfaces constituting the projection lens can be formed as stepped portions that are arranged substantially parallel to the optical axis Z. This arrangement makes it possible to use a portion of light coming from a reflecting surface. This portion of light has not been utilized in a conventional Fresnel lens, which has a circular arc shape as a whole, because the light becomes glare light (light directed upward towards an oncoming driver). As a result, the weight of the lens and lamp can be reduced, and a quantity of light available for lighting to be emitted from the vehicle lamp can be increased without causing glare light.
In the projector type lamp as constituted above, the line constituting at least one of the boundary portions between the plurality of processed projection lens elements may be a circular arc which has its center at a position away from the optical axis of the lamp, or a substantially straight line.
Furthermore, the processed projection lens element, located innermostly with respect to the optical axis center out of the processed projection lens elements, may be so configured that its lens surface appears as a square in a plan view when viewed in the optical axis direction.
The stepped portion between the processed projection lens elements may be colored or covered with a colored member. Thus, the appearance of the headlamp in a non-lighting state can be enhanced and made more original without having an adverse effect on the projection light color.
The short sides of the rectangle of the projection lens may be composed of parts of a circular arc or a contour line of the unprocessed projection lens located outermost. This provides an improved design flexibility.
At least one of the plurality of processed projection lens elements may be replaced by a lens whose longitudinal section has a substantially straight line on its lens surface, which line is substantially perpendicular to the optical axis. Alternatively, it may have a curve which is convex with respect to the optical axis, for providing a predetermined luminous distribution. This provides an appropriate luminous distribution, for example, a distribution in which light is diffused in right and left directions.
Additional features, advantages, and embodiments of the invention may be set forth or apparent from consideration of the following detailed description, drawings, and claims. Moreover, it is to be understood that both the foregoing summary of the invention and the following detailed description are exemplary and intended to provide further explanation without limiting the scope of the invention as claimed.